You dissolve 6g of Co(ClO4)2 (molar mass: 257.83) in 1 liter of water. Assuming the entire sample dissolves, how many individual perchlorate ions are present in this solution?

I'm so lost where to start.

3 answers

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Co(ClO4)2 ==> Co^2+ + 2ClO4^-

You know 1 mole of anything contains 6.02E23 molecules. So how many moles do you have of this stuff. mols = grams/molar mas so
mols = 6/257.83 = ?

So ? x 6.02E23 = number of molecules of Co(ClO4)2. You want to know ClO4^-. There are two of those for every 1 Co(ClO4)2 so there are twice as many of the ClO4^-.
Okay so moles= .0233
0.0233*6.022*10^23=1.403*10^23
1.403*10^23*2=2.806*10^22
Did I get it?